Thermal conductivity gas sensor with amplification material

Abstract

In one example, a thermal conductivity gas sensor is disclosed. The sensor includes a sensing element and an amplification material coupled to the sensing element. The amplification material has a target gas dependent thermal diffusivity. The sensing element measures the thermal diffusivity of the amplification material to determine a target gas concentration.

What is claimed is: 
     
       1. A thermal conductivity gas sensor, comprising:
 a sensing element; 
 an amplification material coupled to the sensing element, and having a target gas dependent thermal diffusivity; and 
 a semiconductor substrate having a cavity, the sensing element being positioned within the cavity, 
 wherein the sensing element measures the thermal diffusivity of the amplification material, 
 wherein the amplification material is positioned around all of the sensing element such that the amplification material encapsulates the sensing element, and 
 wherein the sensing element is a resistive transducer such that the sensing element has a first resistance when the amplification material is exposed to a reference gas and a second resistance when the amplification material is exposed to a target gas. 
 
     
     
       2. The sensor of  claim 1 , further comprising:
 a module which calculates a target gas concentration based on the thermal diffusivity measurement, 
 wherein the sensing element is electrically connected to the module. 
 
     
     
       3. The sensor of  claim 1 , wherein the thermal diffusivity of the amplification material varies more when exposed to a received gas containing the target gas, than does the thermal diffusivity of the received gas varies when exposed to the target gas. 
     
     
       4. The sensor of  claim 1 , wherein the target gas reversibly modifies the thermal diffusivity of the amplification material. 
     
     
       5. The sensor of  claim 4 , wherein the thermal diffusivity of the amplification material is reset to an initial thermal diffusivity by heating the sensing element. 
     
     
       6. The sensor of  claim 4 , further comprising:
 a module which calculates a target gas concentration based on an amount of heat energy required to reset the thermal diffusivity of the amplification material to an initial thermal diffusivity. 
 
     
     
       7. The sensor of  claim 1 , wherein the amplification material is at least one from a group consisting of: an organic bases molecule, a blended amine solvent, and polymer or metal-organic frameworks having an increase in target gas molar density compared to a molar density of the target gas in air. 
     
     
       8. The sensor of  claim 1 , wherein the semiconductor substrate is a silicon substrate, and
 wherein the sensing element includes a sensing wire positioned within the cavity and the amplification material encapsulates a portion of the sensing wire. 
 
     
     
       9. The sensor of  claim 1 , wherein the gas sensor is heated by passing a current through the sensing element. 
     
     
       10. The sensor of  claim 1 , further comprising:
 a heating element, wherein the gas sensor is heated by passing a current through the heating element for bringing the gas sensor into a predetermined temperature equilibrium state before measuring the thermal diffusivity of the amplification material. 
 
     
     
       11. A CMOS gas sensor, comprising:
 a sensing element; 
 an amplification material coupled to the sensing element, and having a target gas dependent thermal diffusivity; and 
 a semiconductor substrate having a cavity, the sensing element being positioned within the cavity, 
 wherein the sensing element has a first resistance when the amplification material is exposed to a reference gas, and 
 wherein the sensing element has a second resistance when the amplification material is exposed to a target gas; and 
 a module converting a difference between the first resistance and the second resistance into a target gas concentration, 
 wherein the amplification material is positioned around all of the sensing element such that the amplification material encapsulates the sensing element, and the sensing element is electrically connected to the module. 
 
     
     
       12. A thermal conductivity gas sensor, comprising:
 a sensing element; 
 an amplification material coupled to the sensing element, and having a target gas dependent thermal diffusivity; and 
 a semiconductor substrate having a cavity, the sensing element being positioned within the cavity, 
 wherein the sensing element measures the thermal diffusivity of the amplification material, 
 wherein the amplification material is deposited on top of the sensing element and seals the top of the cavity without filling the cavity, and 
 wherein the sensing element is a resistive transducer such that the sensing element has a first resistance when the amplification material is exposed to a reference gas and a second resistance when the amplification material is exposed to a target gas. 
 
     
     
       13. A CMOS gas sensor, comprising:
 a sensing element; 
 an amplification material coupled to the sensing element, and having a target gas dependent thermal diffusivity; and 
 a semiconductor substrate having a cavity, the sensing element being positioned within the cavity, 
 wherein the sensing element has a first resistance when the amplification material is exposed to a reference gas, and 
 wherein the sensing element has a second resistance when the amplification material is exposed to a target gas; and 
 a module converting a difference between the first resistance and the second resistance into a target gas concentration, 
 wherein the amplification material is deposited on top of the sensing element and seals the top of the cavity without filling the cavity, and the sensing element is electrically connected to the module.